// oid.h

/*    Copyright 2009 10gen Inc.
 *
 *    This program is free software: you can redistribute it and/or  modify
 *    it under the terms of the GNU Affero General Public License, version 3,
 *    as published by the Free Software Foundation.
 *
 *    This program is distributed in the hope that it will be useful,
 *    but WITHOUT ANY WARRANTY; without even the implied warranty of
 *    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
 *    GNU Affero General Public License for more details.
 *
 *    You should have received a copy of the GNU Affero General Public License
 *    along with this program.  If not, see <http://www.gnu.org/licenses/>.
 *
 *    As a special exception, the copyright holders give permission to link the
 *    code of portions of this program with the OpenSSL library under certain
 *    conditions as described in each individual source file and distribute
 *    linked combinations including the program with the OpenSSL library. You
 *    must comply with the GNU Affero General Public License in all respects
 *    for all of the code used other than as permitted herein. If you modify
 *    file(s) with this exception, you may extend this exception to your
 *    version of the file(s), but you are not obligated to do so. If you do not
 *    wish to do so, delete this exception statement from your version. If you
 *    delete this exception statement from all source files in the program,
 *    then also delete it in the license file.
 */

#pragma once

#include <string>

#include "mongo/base/data_view.h"
#include "mongo/bson/util/builder.h"
#include "mongo/util/time_support.h"

namespace mongo {
    class SecureRandom;

    /**
     * Object ID type.
     * BSON objects typically have an _id field for the object id. This field should be the first
     * member of the object when present. The OID class is a special type that is a 12 byte id which
     * is likely to be unique to the system.  You may also use other types for _id's.
     * When _id field is missing from a BSON object, on an insert the database may insert one
     * automatically in certain circumstances.
     *
     * The BSON ObjectID is a 12-byte value consisting of a 4-byte timestamp (seconds since epoch),
     * in the highest order 4 bytes followed by a 5 byte value unique to this machine AND process,
     * followed by a 3 byte counter.
     *
     *               4 byte timestamp    5 byte process unique   3 byte counter
     *             |<----------------->|<---------------------->|<------------->
     * OID layout: [----|----|----|----|----|----|----|----|----|----|----|----]
     *             0                   4                   8                   12
     *
     * The timestamp is a big endian 4 byte signed-integer.
     *
     * The process unique is an arbitrary sequence of 5 bytes. There are no endianness concerns
     * since it is never interpreted as a multi-byte value.
     *
     * The counter is a big endian 3 byte unsigned integer.
     *
     * Note: The timestamp and counter are big endian (in contrast to the rest of BSON) because
     * we use memcmp to order OIDs, and we want to ensure an increasing order.
     *
     * Warning: You MUST call OID::justForked() after a fork(). This ensures that each process will
     * generate unique OIDs.
     */
    class OID {
    public:

        /**
         * Functor compatible with std::hash for std::unordered_{map,set}
         * Warning: The hash function is subject to change. Do not use in cases where hashes need
         *          to be consistent across versions.
         */
        struct Hasher {
            size_t operator() (const OID& oid) const;
        };

        OID() : _data() {}

        enum {
            kOIDSize = 12,
            kTimestampSize = 4,
            kInstanceUniqueSize = 5,
            kIncrementSize = 3
        };

        /** init from a 24 char hex std::string */
        explicit OID(const std::string &s) {
            init(s);
        }

        /** init from a reference to a 12-byte array */
        explicit OID(const unsigned char (&arr)[kOIDSize]) {
            std::memcpy(_data, arr, sizeof(arr));
        }

        /** initialize to 'null' */
        void clear() { std::memset(_data, 0, kOIDSize); }

        int compare( const OID& other ) const { return memcmp( _data , other._data , kOIDSize ); }

        /** @return the object ID output as 24 hex digits */
        std::string toString() const;
        /** @return the random/sequential part of the object ID as 6 hex digits */
        std::string toIncString() const;

        static OID gen() {
            OID o((no_initialize_tag()));
            o.init();
            return o;
        }

        // Caller must ensure that the buffer is valid for kOIDSize bytes.
        // this is templated because some places use unsigned char vs signed char
        template<typename T>
        static OID from(T* buf) {
            OID o((no_initialize_tag()));
            std::memcpy(o._data, buf, OID::kOIDSize);
            return o;
        }

        static OID max() {
            OID o((no_initialize_tag()));
            std::memset(o._data, 0xFF, kOIDSize);
            return o;
        }

        /** sets the contents to a new oid / randomized value */
        void init();

        /** init from a 24 char hex std::string */
        void init( const std::string& s );

        /** Set to the min/max OID that could be generated at given timestamp. */
        void init( Date_t date, bool max=false );

        time_t asTimeT();
        Date_t asDateT() { return asTimeT() * 1000LL; }

        // True iff the OID is not empty
        bool isSet() const {
            return compare(OID()) != 0;
        }

        /**
         * this is not consistent
         * do not store on disk
         */
        void hash_combine(size_t &seed) const;

        /** call this after a fork to update the process id */
        static void justForked();

        static unsigned getMachineId();  // used by the 'features' command
        static void regenMachineId();

        // Timestamp is 4 bytes so we just use int32_t
        typedef int32_t Timestamp;

        // Wrappers so we can return stuff by value.
        struct InstanceUnique {
            static InstanceUnique generate(SecureRandom& entropy);
            uint8_t bytes[kInstanceUniqueSize];
        };

        struct Increment {
        public:
            static Increment next();
            uint8_t bytes[kIncrementSize];
        };

        void setTimestamp(Timestamp timestamp);
        void setInstanceUnique(InstanceUnique unique);
        void setIncrement(Increment inc);

        Timestamp getTimestamp() const;
        InstanceUnique getInstanceUnique() const;
        Increment getIncrement() const;

        ConstDataView view() const {
            return ConstDataView(_data);
        }

    private:
        // Internal mutable view
        DataView _view() {
            return DataView(_data);
        }

        // When we are going to immediately overwrite the bytes, there is no point in zero
        // initializing the data first.
        struct no_initialize_tag {};
        explicit OID(no_initialize_tag) {}

        char _data[kOIDSize];
    };

    inline std::ostream& operator<<(std::ostream &s, const OID &o) {
        return (s << o.toString());
    }

    inline StringBuilder& operator<<(StringBuilder& s, const OID& o) {
        return (s << o.toString());
    }

    /** Formatting mode for generating JSON from BSON.
        See <http://dochub.mongodb.org/core/mongodbextendedjson>
        for details.
    */
    enum JsonStringFormat {
        /** strict RFC format */
        Strict,
        /** 10gen format, which is close to JS format.  This form is understandable by
            javascript running inside the Mongo server via eval() */
        TenGen,
        /** Javascript JSON compatible */
        JS
    };

    inline bool operator==(const OID& lhs, const OID& rhs) { return lhs.compare(rhs) == 0; }
    inline bool operator!=(const OID& lhs, const OID& rhs) { return lhs.compare(rhs) != 0; }
    inline bool operator<(const OID& lhs, const OID& rhs) { return lhs.compare(rhs) < 0; }
    inline bool operator<=(const OID& lhs, const OID& rhs) { return lhs.compare(rhs) <= 0; }

}  // namespace mongo
